1. Field of the Invention
This invention relates to control apparatus for environmental conditioning systems, and more particularly to simultaneous, central supervisory control of the closed loop operation of individual environmental conditioning systems located in each of several buildings comprising a facility.
2. Description of the Prior Art
As known, HVAC systems are used for controlling the environmental temperature conditions in one or more living spaces within a building enclosure. The HVAC systems include a number of well known types, such as dual duct, multi-zone, and terminal reheat type systems, each including separate sources of heating and cooling within the system.
Each HVAC system is controlled through sensed space temperature signals presented to a local sub-master, or site controller associated with the individual HVAC, the controller providing modulation of the discharge temperatures of the HVAC air handler source in dependence on the sensed temperature signals. The number of living spaces serviced by each HVAC is dependent on the heating and cooling capacity of the system, such that in multi-storied office buildings a number of HVACs may be used to service the living spaces on different floors, or groups of floors. Typically, each HVAC system in the building is controlled by its own controller, autonomously, in dependence on the desired space temperature set into a thermostat within the living space by the human occupant. In response to the need for energy conservation, a number of more recent central control systems have been developed to provide for more efficient control of the individual HVACs within the building. These building control systems typically include a central type of supervisory control over the operation of all of the HVACs within the building. These prior art supervisory controls provided reference temperature values to the HVAC site controls, which in turn regulate the associated HVAC operation through a simple closed loop proportional gain control. This simple proportional gain loop control of the HVAC results in the undesirable characteristics of droop error for too low a gain, and discharge temperature limit cycling within the hot and cold decks for too high a value of proportional gain, as described in the hereinbefore cross referenced application to Games et al (Ser. No. 829,379). Each condition results in energy wasting. In the most recent building supervisory control systems, the central control is provided through a geneal purpose digital computer, connected through transmission lines to the various HVAC systems within the building. One such system is disclosed in a patent to Percoraro et al, U.S. Pat. No. 3,896,871, wherein a computer controlled automated building system includes a central digital computer having programmed routines stored within the computer memory, and which communicates with a number of control points, stated as including environmental equipment, through interconnecting trunk lines and line receives associated with each control point. The computer includes an analog-to-digital (A/D) converter, and although the functional details of the control provided by the computer system of Percoraro over the various control points is not disclosed, it would appear that the computer control is limited to providing discrete analog signals, such as temperature reference signal limits to site controllers associated with the various environmental conditioning equipment, and to monitoring the systems for alarm, or failure conditions. This typifies the level of control known in the art at the present time, i.e. the use of discrete command signals to provide step changes in reference temperatures for "set-back conditions" during unoccupied periods, or for turn on and turn off of the equipment in response to sensed alarm conditions, time of day etc. These types of systems are not fully automated since operator control is required even for routine operation, such as providing a command into the computer requesting the set-back temperature references for nighttime operation. As such, the function of the computer controlled automated building system of Percoraro is that of a "stick control", i.e. allowing an operator in a central control station to provide discrete input control signals to remotely located equipment. The system of Percoraro is further stated as also being applicable for controlling environmental equipment in several buildings in a complex, however, once again the control being limited to discrete control signals.
The demand for operating efficiency, and the difficulty in achieving higher efficiency, is magnified where central control is desired over a number of different types of environmental conditioning systems, each installed in several different buildings located at some distance from each other in a common facility, such as a university campus. These systems may include combinations of HVACs of various types, perimeter heating systems, and thermal sources providing both chill water and steam. In such installations, the degree of control varies as does the type of environmental equipment being controlled. Similarly many systems interact with each other, such as a common chill water or common steam source providing inputs to some number of HVACs in a network servicing a single multi-storied building. In these circumstances it is desirable to control the operation of the HVACs in the network, jointly, in addition to controlling the thermal sources servicing the HVACs, in order that an overall optimization and energy savings may be achieved. This overall control is not possible in the prior art central supervisory systems which provide only discrete control command, i.e. the "stick control" type of system. Similarly, the control of the individual apparatus, i.e. the single HVAC system, perimeter heating system, or thermal source, offers the opportunity for a significant improvement in optimizing operation through the ability to change the control loop gains and reference values, instantly, in response to changes in operating conditions for the particular system. A central control which is capable of optimizing the total operation of interrelated environmental conditioning systems, or of changing the operational gain values of the individual systems, requires a hierarchical control system having the capability of providing direct inner control over the specific functions in each system, while having the capability of managing the overall operation of the entire plurality of conditioning systems in their interrelationship.